Below are three problems dealing with speed and time calculations.

Two buses leaving from two stations 20 km away from each other travel with constant speed of 45km/hr towards each other.Find the time taken to cross each other if the length of each bus is 100m.

a)10sec b)4sec c)15sec d)20sec

Solution :

The time taken to cross each other = (a + b) / (u + v) sec.

Here, a = b = length of the two buses = 100m = 1/10 km.

and u = v = speed of the two buses = 45km/hr.

Time taken to cross each other = (a + b) / (u + v) sec = (1/10 + 1/10) / (45 + 45) hours

1 / (10 x 90) = 1/900 hours.

since 1 hour = 3600 sec, 1/900 hour = 3600/900 = 4 sec

Hence the answer is 4 sec.

A bus starts from A at 7 a.m and reaches the destination B at 7.30 a.m while a cyclist starts from B at 7 a.m and reaches A at 8.30 a.m. At what time the bus and the cyclist will cross each other?

a)7.34 a.m b)7.49 a.m c)7.23 a.m d)8.01 a.m

Solution :

Let the distance …

**Question 1**Two buses leaving from two stations 20 km away from each other travel with constant speed of 45km/hr towards each other.Find the time taken to cross each other if the length of each bus is 100m.

a)10sec b)4sec c)15sec d)20sec

**Answer :**b)4secSolution :

The time taken to cross each other = (a + b) / (u + v) sec.

Here, a = b = length of the two buses = 100m = 1/10 km.

and u = v = speed of the two buses = 45km/hr.

Time taken to cross each other = (a + b) / (u + v) sec = (1/10 + 1/10) / (45 + 45) hours

1 / (10 x 90) = 1/900 hours.

since 1 hour = 3600 sec, 1/900 hour = 3600/900 = 4 sec

Hence the answer is 4 sec.

**Question 2**A bus starts from A at 7 a.m and reaches the destination B at 7.30 a.m while a cyclist starts from B at 7 a.m and reaches A at 8.30 a.m. At what time the bus and the cyclist will cross each other?

a)7.34 a.m b)7.49 a.m c)7.23 a.m d)8.01 a.m

**Answer :**c)7.23a.mSolution :

Let the distance …